MAYBE

Problem:
 rev(nil()) -> nil()
 rev(++(x,y)) -> ++(rev1(x,y),rev2(x,y))
 rev1(x,nil()) -> x
 rev1(x,++(y,z)) -> rev1(y,z)
 rev2(x,nil()) -> nil()
 rev2(x,++(y,z)) -> rev(++(x,rev(rev2(y,z))))

Proof:
 Open